1. Field of the Invention
The invention relates generally to a grommet for a cured in place liner and, more particularly, to a reinforced grommet, method of manufacture and apparatus for its assembly in a liner for installation purposes.
2. Description of the Prior Art
It is generally well known that conduits or pipelines, particularly underground pipes, such as sanitary sewer pipes, storm sewer pipes, water lines and gas lines, that are employed for conducting fluids require repair due to fluid leakage. The leakage may be inward, from the environment into the interior or conducting part of the pipe, or outward, from the conducting part of the pipe into the surrounding environment. Leakage of this type may be due to improper initial installation of the pipe, deterioration of the pipe itself due to normal aging and/or to the effects of conveying corrosive or abrasive materials, cracking of the pipe or of pipe joints due to environmental conditions such as the movement of large vehicles, natural or man made vibrations, or any other such causes. Regardless of the cause, such leakage can result in leakage fluid being conveyed by the pipe, in damage to the surrounding environment and in the possible creation of a dangerous public health hazard.
Because of ever increasing labor and machinery costs, it is becoming increasingly more difficult and less economical to dig up and replace underground pipes, or portions or sections of such underground pipes, that may be leaking. As a result, various methods have been devised for in situ repair or rehabilitation of existing pipes to avoid the expense and hazard associated with digging up and replacing buried pipes or pipe sections. One of the more successful pipe repair or rehabilitation processes that is currently used is identified as the Insituform® Process and is described in U.S. Pat. Nos. 4,009,063; 4,064,211; and 4,135,958, the contents of all of which are incorporated herein in their entirety by reference.
Briefly, in the Insituform Process, an elongated flexible tubular liner of a felt fabric, or foam or similar resin impregnable material that can be impregnated with a thermosetting synthetic catalyzed resin before installation, is installed within an existing pipe. The impregnated liner may then be pulled into the conduit by a rope or cable, and a fluid impermeable inflation bladder or tube is then everted within the liner. Generally, however, the liner is installed utilizing an inverting (or everting) process, as described in the latter two patents.
Normally, the flexible tubular liners have a smooth layer of relatively flexible, substantially impermeable material coating the outside of the liner in its initial state, which impermeable layer ends up on the inside of the liner after the liner is inverted. As the flexible liner, which is impregnated with a resin, is being installed in place within the pipe, the liner is pressurized from within, preferably utilizing a fluid such as water or air, to urge the liner to advance through the pipe and, thereafter, to force the liner radially outwardly to engage and conform to the interior surface of the pipe. The resin is then cured using steam or the like to form a relatively hard, tight fitting, rigid pipe lining that effectively seals any cracks and that repairs any pipe or pipe joint deterioration to prevent further leakage either into or out of the pipe. The cured resin liner also serves to strengthen the existing pipe walls so as to provide added structural support for the surrounding overburden.
Existing liner insertion methods, especially for the installation of a liner into a large diameter pipe, require positive control of the insertion and inversion of the liner throughout the entire inversion process. The known methods for providing the pressure necessary to invert the liner within the pipe and to push it along the length of the pipe must also involve means for controlling the feed rate of the liner, i.e., the rate at which the liner is inverted and pushed into the pipe. Generally, in the Insituform Process, a resin-impregnated liner of a predetermined length and which is typically stored in folded layers, is placed at a manhole adjacent the conduit to be lined, and the leading end of the liner is sealingly clamped to the proximal inside end of an eversion tube in order to create a fluid seal. Pressurized fluid, such as water, air or the like then forces the liner to invert into the conduit. Various means have been provided for controlling the rate at which the liner inverts and is fed along the conduit. The typical means within the Insituform® Process for controlling the “feed rate” of the liner is by restraining the trailing end of the not cured resin-impregnated liner as it is everted into the conduit using a hold-back cable or rope. By restraining the trailing end of the inverting liner, the liner does not invert too quickly, thereby ensuring that the pressure is maintained within the liner.
In addition to being restrained, the trailing end of the liner must also be sealed so that, when the tube is fully everted, the pressurized water, steam or other fluid within the pipe is contained. At times, these pressures can be large. For example, the hold-back force needed during eversion of a 60-inch diameter liner tube with a 30-foot head of water is in excess of 20,000 pounds. When the tube is fully everted, the end of the liner must resist double that force.
Various means have been proposed to secure a hold-back rope or cable to the trailing end of the liner for restraining the trailing end of the liner and for distributing the pulling stress over the entire width of the end of the liner. It has been proposed to seal the liner at the point of attachment of the hold-back cable in order to prevent the fluid within the liner from escaping through the trailing end and penetrating into the resin-wet material of the liner. One such cable end seal is shown in U.S. Pat. No. 4,776,370, the contents of which are incorporated herein in its entirety by reference.
In the process described in U.S. Pat. No. 4,776,370, a short length of cured synthetic resin film, such as “Tuftane”, is bonded directly to the outside of the flattened trailing end of the liner to seal the end of the liner. A series of holes is then formed through the flattened end of the liner. Special plates or straps also having holes are spaced out along both sides of the flattened end of the liner such that those holes align with the holes through the liner. Fastening elements such as nuts and bolts are placed through the holes of both the plates and the liner in order to secure the plates to the liner and seal the end of the liner. The hold-back cable is then attached, either directly or with an additional connector, to the plates for regulating the feed rate of the liner.
Another prior art way of securing a cable or rope to the trailing end of the liner for sealing the end of the liner and for distributing the pulling stress over the entire width of the flattened liner end is to use a series of holes as shown in FIG. 1. In this method a liner 2 having a trailing end 4 is flattened, and a series of holes 6 is formed through liner 2. Metal grommets may optionally be placed in holes 6 as reinforcement. A cable or rope 8 is then woven through holes 6 across liner end 4, and a number of rope handles 10 are looped around cable 8 at the region where cable 8 passes through liner end 4. Handles 10 are then tied to a hold-back cable for restraining trailing end 4 of liner 2 and for controlling the rate of eversion. In both of these conventional methods, the points at which the holes are formed through the liner and at which the handles emerge from the end of the liner must all be sealed in order to prevent water or fluid leakage. The assembly of such sealed ends is time consuming, difficult and expensive, and the seals are rarely totally effective.
In still another prior art way of securing a cable or rope to the trailing end of the liner for sealing the end of the liner and for distributing the pulling stress over the entire width of the flattened liner end is shown in FIG. 2. In this method, which is described in U.S. Pat. No. 5,919,327, the contents of which are incorporated herein in its entirety by reference. Initially holes are cut through the liner, and then resin is impregnated into the region about each hole and hardened to form an integral grommet or reinforcement about the hole. A mold for impregnating the region about the hole with resin includes a lower mold body with a projecting spigot and a groove thereabout. The mold also includes an upper mold body having a central opening with a groove thereabout, where the upper mold body fits over the spigot but leaves room to engage a tube therebetween. A tube fits into the central opening for receiving a resin within it. The resin is forced by a plunger down the tube, about the spigot and into the region surrounding the hole in the liner. After injection, the resin is allowed to harden, thus forming a reinforced hole for attaching a pull-in or hold-back rope or cable. Thereafter, the liner can be folded at the end, and reinforcing disks can be placed on the outside of the folded liner in order to distribute the pulling forces along the material. Also, a capstan can be attached to the integrally-formed grommets between the two folded sides of the liner end portion in order to allow the hold-back cable to be wrapped around it so that, when one end of the cable is fixed, the other end of the cable can be slackened to allow the liner to evert slowly within a conduit.
It remains desirable to provide a grommet for a cured in place liner that is more economical to use and requires fewer parts to form attachment points or reinforced holes for a hold-back or pull-in rope or cable.